// patterns/strategy/StrategyPattern.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// {java patterns.strategy.StrategyPattern}
package strategy;

import java.util.Arrays;
import java.util.List;
import java.util.function.Function;

// The common strategy base type:
class FindMinima {
    Function<List<Double>, List<Double>> algorithm;
}

// The various strategies:
class LeastSquares extends FindMinima {
    LeastSquares() {
        // Line is a sequence of points (Dummy data):
        algorithm = (line) -> Arrays.asList(1.1, 2.2);
    }
}

class Perturbation extends FindMinima {
    Perturbation() {
        algorithm = (line) -> Arrays.asList(3.3, 4.4);
    }
}

class Bisection extends FindMinima {
    Bisection() {
        algorithm = (line) -> Arrays.asList(5.5, 6.6);
    }
}

// The "Context" controls the strategy:
class MinimaSolver {
    private FindMinima strategy;

    MinimaSolver(FindMinima strat) {
        strategy = strat;
    }

    List<Double> minima(List<Double> line) {
        return strategy.algorithm.apply(line);
    }

    void changeAlgorithm(FindMinima newAlgorithm) {
        strategy = newAlgorithm;
    }
}

public class StrategyPattern {
    public static void main(String[] args) {
        MinimaSolver solver =
                new MinimaSolver(new LeastSquares());
        List<Double> line = Arrays.asList(
                1.0, 2.0, 1.0, 2.0, -1.0,
                3.0, 4.0, 5.0, 4.0);
        System.out.println(solver.minima(line));
        solver.changeAlgorithm(new Bisection());
        System.out.println(solver.minima(line));
    }
}
/* Output:
[1.1, 2.2]
[5.5, 6.6]
*/
